I am looking for an alterative to nitric acid for etching silver.
Someone mentioned a solution of ferric nitrate ( as opposed to the
ferric chloride usually used for copper & brass). I happen to have
some that I use for patination.

Is anyone familiar with this process?

The ferric nitrate I have is in powdered form. What kind of
solution works best?

Jeff…the solution of ferric nitrate does work well for etching
sterling and is usually in either powdered or crystal form. The only
rough formula I have found for mixing it is to add enough ferric
nitrate to water (we use distilled because of high mineral content
here) to make the mixture the color of coffee. I have looked through
books but have found no more exact documentation on this.
Donna in WY

I have successfully used ferric nitrate to etch silver.
Unfortunately, I have no specifics as far as measurements etc. I was
told to mix the granular ferric nitrate with water to look like strong
coffee. I warmed the solution a bit and did some tests. I found it
to etch a little quicker than I like. I weakened the solution
slightly and it etched quite smoothly. I used PnP Blue as a resist.
Basically you could say the solution looked like the ferric chloride
one buys at Radio Shack for etching copper. The procedure was also
the same. It’s definitely worth experimenting with. Hope this
helps–Vicki Embrey

I have successfully used Ferric Nitrate to etch silver. The etch is
slow relative to a nitric acid etch, but I like it. I have made the
solution in varying strengths from a medium tea color, to a strong
coffee color. The solution takes a fair bit of ferric nitrate, as I
recall I used about 250 grams to about 200 ml of water for the weaker
solutions. The strong solution will etch in a few hours, the weaker
solutions take a couple of days. ( Note this is for the deeper etch
required for enameling) I follow an enameling champleve protocol most
of the time ( A detailed protocol for Ferric Chloride can be found in
"A Manual of Cloisonn� and Champleve Enameling" by J. Patrick and
Judith Lull Strosahl and Coral Barnhart".

The basic protocol goes like this: make a weak solution in a
container deep enough to fully immerse your piece when stood on end.
Ensure your resist is intact. Place the piece in, (Wear gloves, the
solution is irritating and stains) standing the piece on edge as much
as possible, use an aquarium pump to “bubble” the solution. Check the
condition of your resist and rotate the position of your piece every
few hours. The etch can take up to several days this way, but the
edges are very clean with little undercutting.

How do you dispose of this chemical once you are through with it, and
how toxic is it? My community does not have special pickup days for
possibly toxic compounds (old paint,etc-) that some communities do.
Anne

regarding etching with either ferric chloride or ferric nitrate, I
have been teaching my students to use styrofoam paddles (from American
Science and Surplus) to float the copper or silver (attatched with
double sided carper tape) face down. The styrofoam is boyant enough
to float almost any size of plate and the residue fall straight down.

Proportions of ferric nitrate crystals were approx.:1/2 cup of
crystals to 1 1/2 cups of distilled water.
Donna in WY

Jeff...the solution of ferric nitrate does work well for
etching sterling... I have looked through books but have found no
more exact documentation on this.

The silly answer to “How much…?”, believe it or not, is “Enough!”

All you are interested in here is to have enough nitrate ion
available to combine with the silver to dissolve a little of the
silver to make soluble silver nitrate. So all you have to do is mix
a little ferric nitrate with warm water, immerse your clean and
grease-free silver, and see how it goes. You’ll soon see if there is
enough. Cheers, –
John Burgess; @John_Burgess2 of Mapua Nelson NZ

I do a lot of etching with ferric chloride, and awhile back decided
to try the ferric nitrate on silver. I made up about a cup of solution
and it took about 200 grams of powder to get a medium “coffee” color.
I was not aware of the length of time it apparently takes to etch.
After three hours, there was some etch, but not nearly as much as I’m
used to with the ferric chloride, so I decided to heat the solution.

It was quite a warm day and I was teaching a workshop while running
this experiment, so I ended up placing the covered container in my car
for about another 1 1/2 hours. BAD IDEA! The temperature of the car
interior was over 100 degrees, and I learned that apparently (from the
smell of it) the ferric nitrate will liberate the same noxious
poisonous gas that nitric acid does. I brought the container inside
and took the lid off and it nearly knocked my socks off. So be very
cautious if you heat the stuff, and do it using very good positive
ventilation. (Without heating there were no fumes to speak of.) Nice
etch, though.

Good question about disposal. I haven’t disposed of it yet. I use
the same solution several times–bottle it up in a glass jar with a
plastic lid and keep it in a dark place. I think I’ll ask someone at
Radio Shack since they sell ferric chloride solution–they may have an idea.

How do you dispose of this chemical...(Ferric nitrate)... once
you are through with it, and how toxic is it?

G’day; Ferric nitrate is no more toxic than any other normal
chemical that you treat respectfully. Normal soil contains very
large amounts of iron (ferric) compounds and they don’t do people much
harm - even in the places where there is so much present that the soil
is red with ferric oxide (Utah for instance.) If you are worried about
the silver content of the spent chemical, then just add a little
sodium chloride - table salt - which will precipitate out all the
silver rendering it pretty harmless. Absorb the liquid in sawdust or
shavings and take it to the nearest tip (landfill) or when it has
dried off, wrap it in newspaper and put it with the rest of your
rubbish (trash!) It won’t do anyone or anything any harm. Certainly
nothing nearly like the amount of potential harm of an old car in the
dump! Keeping things in perspective helps widen one’s insight, not
narrows it. Cheers. –
John Burgess; @John_Burgess2 of Mapua Nelson NZ

“So did the heat help the etching process? Would you heat again with
ferric nitrate (with good ventilation of course)?”

The heat sped up the etching process considerably. But the fumes were
so noxious that I don’t think I want to bother with heating it, even
though I have a hood. I tried the process as an alternative to nitric
acid, because I wanted to avoid the fumes of the nitric, so if the
fumes are just as bad there isn’t anything gained. And the ferric
nitrate is pretty pricey for as much as it takes and as long as it
takes. The nitric goes a lot longer for the money. But I’ve heard the
etch with the ferric is much cleaner, with no underbiting. Also, I was
using PnP and it held up pretty well. I’ve never tried PnP with nitric
acid, so have no experience to compare with, but I’ve heard it
doesn’t hold up very well. So this might be a reason to use the
ferric, if the transfer process interests you.

I am still interested in using the ferric nitrate with a rectifier.
My first attempt at electroetching was a dismal failure (nothing
happened). Is there anyone who can shed some light on the specifics of
this process?

Rene–I got the on using Ferric Nitrate with a rectifier
from orchid in Aug. 1998. It may be in the archives, but I’ll print
it here. Thank goodness I printed it out as my computer crashed
shortly after. It came from Anne Hollerbach (I’ll quote directly):

I use my anodizer to get a faster etch. This was an idea that
Charles Lewton-Brain discussed at a bench tips free-for-all at SNAG
’97. He suggested using electricity to speed up reactions, and this
really does work. I use a titanium cathode in my ferric nitrate bath,
and the piece to be etched is the anode. The amazing thing is how
little voltage it takes to make a huge differenc: I never go higher
than 20V, and usually work at 10V. For some of my applications, I
have been able to get an etch in 45 - 90 seconds that used to take
nearly 4 hours. And the quality is better because the resist isn’t
sitting in the bath all that time getting ratty around the edges.
Note: don’t do this with ferric chloride since the electricity will
break down the chemical and you will get chlorine gas which is toxic
to you.

By the way there is a happy medium to heating the ferric nitrate. If
it is warm-not hot-there doesn’t seem to be the fumes you describe and
it etches faster. I got a nice etch in an hour by using warm water to
mix the crystals and placing the pan on one of those microwave hot
plates. Basically, the hot plate is a piece of granite like material
on a plastic tray which you heat in the microwave for one minute.
It’s supposed to keep hot food hot, so I thought I’d try it this way.
Got it at the local dollar store!

Vicki, thanks for posting the details about the ferric nitrate etch
using the rectifier. Is it necessary to use a titanium cathode? Also,
I’m glad to know about your experience with warming the ferric nitrate
a little but not too much. Makes sense.

Lingering question: is there any alternative way (which doesn’t
liberate chlorine gas) to use a rectifier to get a deep etch on copper
using ferric chloride, for purposes of champlev� enameling? This is
actually what I’d tried which didn’t work. I was working at 5 to 10V,
with large piece of copper as cathode.